Amazon calculates a product's star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers and factors that establish reviewer trustworthiness.
I have a regular medium frame, and it fit me perfectly. A wee bit loose, but good to throw on over something you're wearing and just walk out. It's also thick, pretty warm for a sweatshirt. Woolly feel.